package io.tec.cloud.algorithm.c04_v20220613;

/**
 * 在一个数组中，一个数左边比它小的数的总和，叫数的小和，所有数的小和累加起来，叫数组小和。求数组小和。
 * 例子： [1,3,4,2,5]
 * 1左边比1小的数：没有
 * 3左边比3小的数：1
 * 4左边比4小的数：1、3
 * 2左边比2小的数：1
 * 5左边比5小的数：1、3、4、 2
 * 所以数组的小和为1+1+3+1+1+3+4+2=16
 */
public class Code02_SmallSum {

    public static int smallSum(int[] arr) {
        if (arr == null || arr.length < 2) {
            return 0;
        }

        int L = 0;
        int R = arr.length - 1;

        return process(arr, L, R);
    }

    private static int process(int[] arr, int L, int R) {
        if (L == R) {
            return 0;
        }
        int mid = L + ((R - L) >> 1);
        return process(arr, L, mid) + process(arr, mid + 1, R) + merge(arr, L, mid, R);
    }

    private static int merge(int[] arr, int L, int mid, int R) {
        int sum = 0;
        int[] help = new int[R - L + 1];
        int idx = 0;
        int li = L;
        int ri = mid + 1;
        while (li <= mid && ri <= R) {
            // 看我右边有多少个数字比我大：相同时，复制右边的
            if (arr[li] < arr[ri]) {
                sum += arr[li] * (R - ri + 1);
                help[idx++] = arr[li++];
            } else {
                help[idx++] = arr[ri++];
            }
        }

        while (li <= mid) {
            help[idx++] = arr[li++];
        }

        while (ri <= R) {
            help[idx++] = arr[ri++];
        }

        for (int i = 0; i < help.length; i++) {
            arr[L + i] = help[i];
        }
        return sum;
    }

    public static int smallSum2(int[] arr) {
        if (arr == null || arr.length < 2) {
            return 0;
        }

        int sum = 0;
        int N = arr.length;
        int mergeSize = 1;
        while (mergeSize < N) {
            int L = 0;
            while (L < N) {
                if (mergeSize >= N - L) {
                    return 0;
                }
                int mid = L + mergeSize - 1;
                int R = mid + Math.min(mergeSize, N - 1 - mid);
                sum += merge(arr, L, mid, R);
                L = R + 1;
            }
            if (mergeSize > N / 2) {
                break;
            }
            mergeSize <<= 1;
        }
        return sum;
    }


    // for test
    public static int comparator(int[] arr) {
        if (arr == null || arr.length < 2) {
            return 0;
        }
        int res = 0;
        for (int i = 1; i < arr.length; i++) {
            for (int j = 0; j < i; j++) {
                res += arr[j] < arr[i] ? arr[j] : 0;
            }
        }
        return res;
    }

    // for test
    public static int[] generateRandomArray(int maxSize, int maxValue) {
        int[] arr = new int[(int) ((maxSize + 1) * Math.random())];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
        }
        return arr;
    }

    // for test
    public static int[] copyArray(int[] arr) {
        if (arr == null) {
            return null;
        }
        int[] res = new int[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i] = arr[i];
        }
        return res;
    }

    // for test
    public static boolean isEqual(int[] arr1, int[] arr2) {
        if ((arr1 == null && arr2 != null) || (arr1 != null && arr2 == null)) {
            return false;
        }
        if (arr1 == null && arr2 == null) {
            return true;
        }
        if (arr1.length != arr2.length) {
            return false;
        }
        for (int i = 0; i < arr1.length; i++) {
            if (arr1[i] != arr2[i]) {
                return false;
            }
        }
        return true;
    }

    // for test
    public static void printArray(int[] arr) {
        if (arr == null) {
            return;
        }
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }
        System.out.println();
    }

    // for test
    public static void main(String[] args) {
        int testTime = 1000000;
        int maxSize = 3;
        int maxValue = 100;
        boolean succeed = true;
        for (int i = 0; i < testTime; i++) {
            int[] arr1 = generateRandomArray(maxSize, maxValue);
            int[] arr2 = copyArray(arr1);
            if (smallSum2(arr1) != comparator(arr2)) {
                succeed = false;
                printArray(arr1);
                printArray(arr2);
                break;
            }
        }
        System.out.println(succeed ? "Nice!" : "Fucking fucked!");
    }

}
